Stir together soy sauce, sesame oil, mirin, and honey in a small bowl. Pour half into a separate small bowl, stir in rice wine vinegar, and set it aside as a dipping sauce.
Spread sesame seeds out on a plate. Coat tuna steaks with remaining soy sauce mixture, then press into sesame seeds to coat.
Heat olive oil in a cast iron skillet over high heat until very hot. Place steaks in the pan; sear for about 30 seconds on each side. Serve with dipping sauce and wasabi paste.
